I was just thinking about how much I refer to this book in any course that I teach (I teach Microsoft Office applications to business staff) - yesterday I was talking about it in a Powerpoint Course, last week it was in a Publisher course.
It's a great book. I first saw it about 10 years ago and have been a fan ever since.
Using basic design principles of C(ontext) R(epetition) A(lignment) and P(roximity), she makes it very clear how to put together a design piece. This is done through showing an example (usually of a phone book ad) which looks OK, and then explaining whats wrong with it, then presenting the same ad again with corrections applied, the results are certainly worth it.
I can't recommend it highly enough - you can read about it at Amazon here -
The Non-Designer's Design Book by Robin Williams (Paperback - Sep 15, 2003) - 2nd ed. So there you go. If you ever wanted a design book, this is the one.